Cross-linkable copolymers and hydrogels

ABSTRACT

The present invention describes novel statistical copolymers and the preparation and possible uses thereof. Copolymers are described that are water-soluble and cross-linkable and that comprise the copolymerization product of a monomer mixture consisting substantially of a vinyl lactam (a) and at least one further vinyl monomer (b) of a different type selected from the group consisting of hydrophobic, hydrophilic and functional vinyl monomers, wherein the monomers are present in the copolymer in the form of statistically distributed building blocks, and, if a functional vinyl monomer is present as a building block in the copolymer, that building block is, where appropriate, modified with a reactive vinyl monomer (c), the reactive vinyl monomer (c) being linked to a building block of a functional vinyl monomer with retention of its vinylic group and with the formation of a covalent bond.

This application is a division of U.S. Ser. No. 08/942,097 filed Oct. 1,1997, which is now U.S. Pat. No. 5,936,052, which is a division of U.S.Ser. No. 08/339,384 filed Nov. 4, 1994, which is now U.S. Pat. No.5,712,356.

The present invention relates to novel copolymers based on vinyllactams, the monomer building blocks of which have a statisticaldistribution, that are water-soluble and cross-linkable, and are, whereappropriate, modified with reactive vinyl monomers, to processes for thepreparation of the novel copolymers, to cross-linked water-insolublecopolymers, hydrogels and mouldings produced from the cross-linkedwater-insoluble copolymers, especially contact lenses, and to processesfor the preparation of hydrogels and finished contact lenses using thesaid cross-linkable water-soluble copolymers.

Vinyl lactam copolymers, such as, for example, vinylpyrrolidonecopolymers, have already been known for a relatively long time asmaterial for contact lenses having a high water content. Scafilcon A andSurfilcon A are mentioned here as representative examples. They haveproved very successful in practice owing to their high degree of wearercomfort.

U.S. Pat. No. 4,347,198 describes the manufacture of contact lenseswhere a hydrophilic component, for example N-vinylpyrrolidone, ahydrophobic component, for example methyl methacrylate, a cross-linkingagent and an initiator are mixed in a solvent, for example DMSO, andthen the whole is cross-linked in a mould. After extraction andequilibration in water, a soft hydrogel contact lens is obtained.Extraction with water is necessary because the solvent and unreactedvinyl monomers have to be removed. Since a polymer swells to differentextents, for example in DMSO on the one hand and water on the other, thecontact lens assumes its final size only at that stage.

EP 216 074 describes a process for the preparation of hydrogel contactlenses. There, a methacrylate-modified polyvinyl alcohol is used whichis copolymerised in DMSO solution with vinyl monomers in a suitablecasting mould, for example in the presence of a photoinitiator byirradiation with UV light for approximately 3 hours. After being removedfrom the mould, the contact lens is extracted with water orphysiological saline solution in order to remove the DMSO and unreactedvinyl monomers. In this case too, the contact lens does not receive itsfinal geometry until the final stage owing to the different influencesof DMSO and water on its swelling behaviour.

Efforts are being made in various quarters to reduce the reaction timesin polymer preparation in order to make lens manufacture moreeconomical. EP 370 827 (Vistakon) describes, for example, the use ofboric acid esters of certain difunctional alcohols as solvents for thepolymerisation of, in the main, HEMA in a polystyrene casting mould.Polymerisation takes place in only 6 to 12 minutes, again in thepresence of a photo-initiator by irradiation with UV light, and yields agel which then has to be extracted with water.

One disadvantage of the previous processes for the manufacture ofcontact lenses is the laborious extraction with water or physiologicalsaline solution, which precludes economical contact lens manufacturewith short cycle times.

Another disadvantage of the previous processes is, as already mentioned,the relatively slow cross-linking speed in the preparation of polymersin the case of the prior art.

The present invention provides a remedy for those problems since itdiscloses statistical copolymers that are water-soluble andcross-linkable. The above-mentioned laborious extraction with water orphysiological saline solution after cross-linking is omitted in the caseof the present invention because cross-linking can be effected, forexample, in water. The disadvantage of the relatively slow cross-linkingspeed is countered by using copolymers instead of monomers as startingmaterial for the manufacture of contact lenses.

The present invention accordingly relates to a water-solublecross-linkable copolymer comprising a copolymerisation product of amonomer mixture consisting substantially of a vinyl lactam (a) and atleast one further vinyl monomer (b) of a different type selected fromthe group consisting of hydrophobic, hydrophilic and functional vinylmonomers, wherein the monomers are present in the copolymer in the formof statistically distributed building blocks, and, if a functional vinylmonomer is present as a building block in the copolymer, that buildingblock is, where appropriate, modified with a reactive vinyl monomer (c),the reactive vinyl monomer (c) being linked to a building block of afunctional vinyl monomer with retention of its vinylic group and withthe formation of a covalent bond.

Within the context of the present invention, any reference hereinbeforeor hereinafter to a copolymer is always intended to mean a copolymerwherein the monomers are present in the form of statisticallydistributed building blocks.

A copolymer wherein the monomers are present in the form ofstatistically distributed building blocks is to be understood as being acopolymer comprising at least two different types of monomer in the caseof which, in 98% of all cases, the block size of identical monomerbuilding blocks is in the range of from 1 to 10, preferably in 90% ofall cases in the range of from 1 to 7 and more preferably in 80% of allcases in the range of from 1 to 5. Within the context of the presentinvention, the expression “statistical monomer distribution in acopolymer” or the expression “statistical copolymer” is also used tohave the same meaning. A statistical monomer distribution in a copolymeralso means that said copolymer is substantially free of homopolymers andblock polymers. Statistical copolymers differ in their physicalproperties from their isomeric homopolymers and block polymers and can,if necessary, accordingly be separated therefrom by physical methods.Statistical copolymers are given their typical characterising features,for example, by their molecular weights, their solubilities, theirthermal properties or their NMR spectra

Statistical copolymers can be distinguished from non-statisticalcopolymers, for example, on the basis of the molecular weightdistribution. Statistical copolymers generally exhibit a typicalGaussian molecular weight distribution while non-statistical copolymersdo not. The molecular weight range of a statistical copolymer isgenerally adjustable and depends, inter alia, on the nature and amountof the solvent used. The average molecular weight can be adjusted, forexample, to a range of from 1·10⁵ to 4·10⁵, for example whencopolymerisation is carried out in methanol.

In the present invention, preference is given to copolymers according toclaim 1 that comprise a copolymerisation product of a monomer mixtureconsisting of 30-95 mol % of a vinyl lactam (a) and 5-70 mol % of atleast one vinyl monomer (b) and, where appropriate, a reactive vinylmonomer (c).

A preferred copolymer is a copolymer according to claim 1 that comprisesa copolymerisation product of a monomer mixture consisting of 50-90 mol% of a vinyl lactam (a) and 10-50 mol % of at least one vinyl monomer(b) and, where appropriate, a reactive vinyl monomer (c).

More strongly preferred is a copolymer according to claim 1 thatcomprises a copolymerisation product of a monomer mixture consisting of60-80 mol % of a vinyl lactam (a) and 20-40 mol % of at least one vinylmonomer (b) and, where appropriate, a reactive vinyl monomer (c).

The present invention relates preferably also to a copolymer accordingto claim 2 wherein the proportion of reactive vinyl monomer (c) is up to50 mol % of the total amount of vinyl monomer (b) and (c).

Also preferred is a copolymer according to claim 3 wherein theproportion of reactive vinyl monomer (c) is from 5 to 40 mol % of thetotal amount of vinyl monomer (b) and (c).

Preference is given also to a copolymer according to claim 4 wherein theproportion of reactive vinyl monomer (c) is from 10 to 25 mol % of thetotal amount of vinyl monomer (b) and (c).

In the case of commercial lenses, the hydrophobic vinyl monomer used isprincipally methyl methacrylate (MMA). MMA can also be used in thepresent invention. In general, however, it is possible to use any vinylmonomer that, as a copolymer with a vinyl lactam, yields an opticallyclear and mechanically stable hydrogel.

A vinyl lactam (a) according to the invention is understood as being,for example, a five-to seven-membered lactam of formula I

wherein

R is an alkylene bridge having from 2 to 8 carbon atoms,

R₁ is hydrogen, alkyl, aryl, aralkyl or alkaryl, preferably hydrogen orlower alkyl having up to 7 and, more preferably, up to 4 carbon atoms,such as, for example, methyl, ethyl or propyl; aryl having up to 10carbon atoms, and also aralkyl or alkaryl having up to 14 carbon atoms;and

R₂ is hydrogen or lower alkyl having up to 7 and, more preferably, up to4 carbon atoms, such as, for example, methyl, ethyl or propyl.

Some N-vinyl lactams (a) corresponding to the above structural formula Iare N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-2-caprolactam,N-vinyl-3-methyl-2-pyrrolidone, N-vinyl-3-methyl-2-piperidone,N-vinyl-3-methyl-2-caprolactam, N-vinyl-4-methyl-2-pyrrolidone,N-vinyl-4-methyl-2-caprolactam, N-vinyl-5-methyl-2-pyrrolidone,N-vinyl-5-methyl-2-piperidone, N-vinyl-5,5-dimethyl-2-pyrrolidone,N-vinyl-3,3,5-trimethyl-2-pyrrolidone,N-vinyl-5-methyl-5-ethyl-2-pyrrolidone,N-vinyl-3,4,5-trimethyl-3-ethyl-2-pyrrolidone,N-vinyl-6-methyl-2-piperidone, N-vinyl-6-ethyl-2-piperidone,N-vinyl-3,5-dimethyl-2-piperidone, N-vinyl-4,4-dimethyl-2-piperidone,N-vinyl-7-methyl-2-caprolactam, N-vinyl-7-ethyl-2-caprolactam,N-vinyl-3,5-methyl-2-caprolactam, N-vinyl-4,6-dimethyl-2-caprolactam andN-vinyl-3,5,7-trimethyl-2-caprolactam. If desired, mixtures thereof mayalso be used.

A preferably used vinyl lactam (a) is a heterocyclic monomer of formulaI containing from 4 to 6 carbon atoms in the heterocyclic ring.

A further preferably used vinyl lactam (a) is a heterocyclic monomer offormula I containing 4 carbon atoms in the heterocyclic ring.

A vinyl lactam (a) whose use is more strongly preferred is aheterocyclic monomer of formula I containing 4 carbon atoms in theheterocyclic ring and wherein R₁ is hydrogen or lower alkyl.

A vinyl lactam (a) whose use is likewise more strongly preferred is aheterocyclic monomer of formula I containing 4 carbon atoms in theheterocyclic ring and wherein R₁ and R₂ are each independently of theother hydrogen or lower alkyl.

A strongly preferred vinyl lactam (a) is N-vinyl-2-pyrrolidone.

A vinyl monomer (b) present in a copolymer according to the inventionmay be hydrophilic, hydrophobic, functional or a mixture of the three.Suitable vinylic monomers include especially those customarily used inthe manufacture of contact lenses.

Hydrophobic vinylic monomers (b) are understood as being monomers thattypically yield as homopolymers polymers that are water-insoluble andcan absorb less than 10% by weight water.

Analogously, a hydrophilic vinylic monomer (b) is understood as being amonomer that typically yields as homopolymer a polymer that iswater-soluble or can absorb at least 10% by weight water.

Suitable hydrophobic vinylic monomers (b) include, without this listbeing definitive, C₁-C₁₈alkyl and C₃-C₁₈cycloalkyl acrylates andmethacrylates, C₃-C₁₈alkyl-acrylamides and -methacrylamides,acrylonitrile, methacrylonitrile, vinyl-C₁-C₁₈alkanoates,C₂-C₁₈-alkenes, C₂-C₁₈haloalkenes, styrene, lower alkylstyrene, loweralkyl vinyl ethers, C₂-C₁₀-perfluoroalkyl acrylates and methacrylates,or acrylates and methacrylates partially fluorinated in a correspondingmanner, C₃-C₁₂perfluoroalkyl-ethyl-thiocarbonylaminoethyl acrylates andmethacrylates, acryloxy- and methacryloxy-alkylsiloxanes,N-vinyl-carbazole, C₁-C₁₂alkyl esters of maleic acid, fumaric acid,itaconic acid, mesaconic acid and the like. Preferred are, for example,C₁-C₄alkyl esters of vinylically unsaturated carboxylic acids havingfrom 3 to 5 carbon atoms or vinyl esters of carboxylic acids having upto 5 carbon atoms.

Examples of suitable hydrophobic vinylic monomers include methylacrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate,cyclohexyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethylmethacrylate, propyl methacrylate, vinyl acetate, vinyl propionate,vinyl butyrate, vinyl valerate, styrene, chloroprene, vinyl chloride,vinylidene chloride, acrylonitrile, 1-butene, butadiene,methacrylonitrile, vinyltoluene, vinyl ethyl ether,perfluorohexylethylthiocarbonylaminoethyl methacrylate, isobornylmethacrylate, trifluoroethyl methacrylate, hexafluoroisopropylmethacrylate, hexafluorobutyl methacrylate,tris-trimethylsilyloxy-silyl-propyl methacrylate,3-methacryloxypropylpentamethyldisiloxane andbis(methacryloxypropyl)tetramethyldisiloxane.

Preferred examples of hydrophobic vinylic monomers (b) are methylmethacrylate and ethyl methacrylate.

Suitable hydrophilic vinylic monomers (b) include, without this listbeing definitive, hydroxy-substituted lower alkyl acrylates andmethacrylates, acrylamide, methacrylamide, lower alkyl-acrylamides and-methacrylamides, ethoxylated acrylates and methacrylates,hydroxy-substituted lower alkyl-acrylamides and -methacrylamides,hydroxy-substituted lower alkyl vinyl ethers, sodium ethylenesulfonate,sodium styrenesulfonate, 2-acrylamido-2-methylpropanesulfonic acid,N-vinylpyrrole, 2- and 4-vinylpyridine, vinylically unsaturatedcarboxylic acids having a total of from 3 to 5 carbon atoms, amino-loweralkyl (the term “amino” also including quaternary ammonium), mono-loweralkylamino-lower alkyl and di-lower alkylamino-lower alkyl acrylates andmethacrylates, allyl alcohol and the like. Preferred are, for example,hydroxy-substituted lower alkyl acrylates and methacrylates,hydroxy-substituted lower alkyl-acrylamides and -methacrylamides andvinylically unsaturated carboxylic acids having a total of from 3 to 5carbon atoms.

Examples of suitable hydrophilic vinylic monomers (b) includehydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropylacrylate, ammonium ethyl methacrylate hydrochloride, acrylamide,methacrylamide, dimethylacrylamide, allyl alcohol, vinylpyridine,glycerol methacrylate, N-(1,1-dimethyl-3-oxobutyl)acrylamide, acrylicacid, methacrylic acid and the like.

Preferred hydrophilic vinylic monomers (b) are 2-hydroxyethylmethacrylate, acrylic acid, methacrylic acid and ammonium ethylmethacrylate hydrochloride.

A functional vinyl monomer (b) is a monomer that carries in addition tothe vinyl group a functional group, such as, for example, hydroxy,amino, lower alkyl-substituted amino, carboxyl, esterified carboxyl,preferably lower alkoxycarbonyl, epoxy or sulfo (—SO₃H). The functionalgroup is retained after copolymerisation and can be used forafter-treatment or preferably for a modification of the copolymer.

Suitable functional vinyl monomers (b) that can be used are, forexample, without this list being definitive, hydroxy-substituted loweralkyl acrylates and methacrylates, ethoxylated acrylates andmethacrylates, epoxy-lower alkyl acrylates and methacrylates,epoxycycloalkyl-lower alkyl acrylates and methacrylates,hydroxy-substituted lower alkyl-acrylamides and -methacrylamides,hydroxy-substituted lower alkyl vinyl ethers, amino- orhydroxy-substituted styrenes, sodium ethylenesulfonate, sodiumstyrenesulfonate, 2-acrylamido-2-methylpropanesulfonic acid, acrylicacid, methacrylic acid, amino-lower alkyl (the term “amino” alsoincluding quaternary ammonium) and mono-lower alkylamino-lower alkylacrylates and methacrylates, acryloxy- and methacryloxy-loweralkylmaleimides and allyl alcohol.

Examples of functional vinyl monomers are 2-hydroxyethyl methacrylate,3-hydroxypropyl methacrylate, acrylic acid, methacrylic acid,4-aminostyrene, 3-methacryloxymethyl-7-oxa-bicyclo[4.1.0]heptane(CHOMA), N-methacryloxyethyl-maleimide (DMI-O-MA), glycidyl methacrylate(GMA), ammonium ethyl methacrylate hydrochloride (AEMA) or ammoniumpropyl methacrylate hydrochloride (APMA).

Preferred functional vinyl monomers (b) are 2-hydroxyethyl methacrylateand ammonium ethyl methacrylate hydrochloride (AEMA).

A reactive vinyl monomer (c) is understood as being a monomer thatcarries a reactive group in addition to the vinyl group. A reactivevinyl monomer (c) is used for the modification of a copolymer afterpolymerisation, the reactive group of a monomer (c) reacting with afunctional group present in the copolymer to form a covalent bond andthe vinylic group of the monomer (c) being retained. A condition for themodification of a copolymer according to the invention is that afunctional monomer (b) should be present as a building block in thementioned copolymer.

Suitable as reactive vinyl monomer (c) are, for example,hydroxy-substituted lower alkyl acrylates and methacrylates,hydroxy-substituted lower alkyl-acrylamides and -methacrylamides,hydroxy-substituted lower alkyl vinyl ethers,2-acrylamido-2-methylpropanesulfonic acid, amino-lower alkyl (the term“amino” also including quaternary ammonium) and mono-loweralkylamino-lower alkyl acrylates and methacrylates, allyl alcohol,epoxy-lower alkyl acrylates and methacrylates, isocyanato-lower alkylacrylates and methacrylates, vinylically unsaturated carboxylic acidshaving from 3 to 7 carbon atoms and also the acid chlorides andanhyrides thereof, amino-, hydroxy- or isocyanate-substituted styrenesand epoxycycloalkyl-lower alkyl acrylates and methacrylates.

Examples of suitable reactive vinyl monomers (c) include, inter alia,hydroxyethyl acrylate and methacrylate, hydroxypropyl acrylate andmethacrylate, allyl alcohol, glycerol methacrylate, acrylic acid,acrylic acid chloride, methacrylic acid, methacrylic acid chloride,4-aminostyrene, 3-methacryloxymethyl-7-oxa-bicyclo[4.1.0]heptane(CHOMA), isocyanatoethyl acrylate and methacrylate, glycidylmethacrylate (GMA), ammonium ethyl methacrylate hydrochloride (AEMA) andammonium propyl methacrylate hydrochloride (APMA).

Preferred reactive vinyl monomers (c) are hydroxyethyl acrylate andmethacrylate, hydroxypropyl acrylate and methacrylate, isocyanatoethylacrylate and methacrylate, acrylic and methacrylic acid chloride,ammonium ethyl methacrylate hydrochloride (AEMA) and ammonium propylmethacrylate hydrochloride (APMA).

Within the context of this invention, the term “lower” used inconnection with radicals and compounds means, unless defined otherwise,especially radicals or compounds having up to 7 carbon atoms, preferablyhaving up to 4 carbon atoms.

Lower alkyl has especially up to 7 carbon atoms, preferably up to 4carbon atoms, and is, for example, methyl, ethyl, propyl, butyl ortert-butyl.

Aryl is, for example, naphthyl, pyridyl, thienyl or preferably phenylthat is unsubstituted or substituted by lower alkyl or by lower alkoxy.

Lower alkoxy has especially up to 7 carbon atoms, preferably up to 4carbon atoms, and is, for example, methoxy, ethoxy, propoxy ortert-butoxy.

Aralkyl is preferably phenyl-lower alkyl having up to 4 carbon atoms inthe alkyl unit, for example 1- or 2-phenylethyl or benzyl.

Alkaryl is preferably lower alkylphenyl having up to 4 carbon atoms inthe alkyl unit, for example ethylphenyl or tolyl.

Cycloalkyl has especially up to 7 carbon atoms, preferably from 3 to 6carbon atoms, and is, for example, cyclopropyl, cyclobutyl, cyclopentylor cyclohexyl.

The present invention relates also to statistical copolymers wherein themonomer building blocks are selected from vinyl lactam (a) that is aheterocyclic monomer of formula I having 4 carbon atoms in theheterocyclic ring, and from vinyl monomer (b) that is unsubstituted orhydroxy-substituted C₁-C₁₈alkyl acrylate or methacrylate, loweralkylacrylamide or -methacrylamide or allyl alcohol.

Other monomer building blocks preferably used in a copolymer accordingto the invention are, for example, a vinyl lactam (a) that is aheterocyclic monomer of formula I containing 4 carbon atoms in theheterocyclic ring, and a vinyl monomer (c) selected from amino-loweralkyl and mono-lower alkyl-amino-lower alkyl acrylates andmethacrylates, epoxy-lower alkyl acrylate and methacrylate and avinylically unsaturated carboxylic acid having from 3 to 7 carbon atomsand also the acid chlorides and anhydrides thereof.

Further monomer building blocks preferably used in a copolymer accordingto the invention are, for example, a vinyl lactam (a) that is aheterocyclic monomer of formula I containing 4 carbon atoms in theheterocyclic ring, a vinyl monomer (b) selected from unsubstituted andhydroxy-substituted C₁-C₁₈alkyl acrylate and methacrylate, amino-loweralkyl and mono-lower alkylamino-lower alkyl acrylate and methacrylate,and a vinyl monomer (c) selected from epoxy-lower alkyl acrylate andmethacrylate, isocyanato-lower alkyl acrylate and methacrylate and avinylically unsaturated carboxylic acid having from 3 to 7 carbon atomsand also the acid chloride and anhydride thereof.

Other monomer building blocks preferably used in a copolymer accordingto the invention are, for example, vinylpyrrolidone, a vinyl monomer (b)selected from hydroxy-substituted C₁-C₁₈alkyl acrylate and methacrylate,and a vinyl monomer (c) selected from amino-lower alkyl and mono-loweralkyl-amino-lower alkyl acrylate and methacrylate, epoxy-lower alkylacrylate and methacrylate and a vinylically unsaturated carboxylic acidhaving from 3 to 7 carbon atoms and also the acid chloride and anhydridethereof.

Other monomer building blocks preferably used in a copolymer accordingto the invention are, for example, vinylpyrrolidone, a monomer (b)selected from hydroxyethyl methacrylate and hydroxypropyl methacrylate,and a vinyl monomer (c) selected from amino-lower alkyl and mono-loweralkylamino-lower alkyl acrylate and methacrylate and epoxy-lower alkylacrylate and methacrylate.

Other monomer building blocks preferably used in a copolymer accordingto the invention are, for example, vinylpyrrolidone, a monomer (b)selected from methyl methacrylate, hydroxyethyl methacrylate andhydroxypropyl methacrylate, and a vinyl monomer (c) selected fromglycidyl methacrylate (GMA), isocyanatoethyl methacrylate, ammoniumethyl methacrylate hydrochloride (AEMA) and ammonium propyl methacrylatehydrochloride (APMA).

Other monomer building blocks preferably used in a copolymer accordingto the invention are, for example, vinylpyrrolidone, a monomer (b)selected from methyl methacrylate, N,N-dimethylmethacrylamide, ammoniumethyl methacrylate hydrochloride (AEMA), ammonium propyl methacrylatehydrochloride (APMA), hydroxyethyl methacrylate and hydroxypropylmethacrylate, and a vinyl monomer (c) selected from glycidylmethacrylate (GMA), isocyanatoethyl methacrylate (IEM) and methacrylicacid.

The present invention relates also to a process for the preparation of astatistical copolymer.

In order to synthesise a copolymer with a statistical distribution ofthe monomer building blocks, it is necessary to take into account thecopolymerisation parameters of the monomers used. The present inventionis concerned with a process for the synthesis of statistical copolymerstaking into account the Lewis-Mayo theory.

The copolymer composition can be calculated from the copolymerisationparameters and from the monomer composition, or the necessary monomercomposition can be calculated from the desired copolymer composition andthe copolymerisation parameters, in accordance with the Lewis-Mayoequation.

The Lewis-Mayo equation is as follows:

F₁/F₂=((r₁·M₁)+M₂)/((r₂·M₂)+M₁), wherein the following meanings apply:

F₁/F₂=ratio of the monomer building blocks in the copolymer,

M₁; M₂=instantaneous monomer concentrations in the reaction vessel,

r₁=k₁₁/k₁₂; r₂=k₂₂/k₂₁ copolymerisation parameters which can be takenfrom books of tables,

k_(ij) wherein i=1,2 and j=1,2 speed constants of the reactions ofradical i with monomer j.

A process for the preparation of a statistical copolymer ischaracterised by the following description. A monomer mixture I, thecomposition of which gives the desired copolymer composition inaccordance with the Lewis-Mayo equation, is placed in a reaction vesseland polymerisation is initiated, for example with a thermal initiator(for example AIBN). After polymerisation has been initiated, a monomermixture II is metered in, the composition of which corresponds to thedesired copolymer composition. The metering speed is in accordance withthe consumption of the monomers. The following conditions must beobserved in the reaction vessel:

dM₁/dt=dM₂/dt=0 and dM₁/dM₂=const.; this means that the concentration ofthe monomers must remain the same during the reaction and their ratio isto be constant. Those conditions can be met in two ways:

1. Since the initiator concentration decreases in accordance withfirst-order kinetics and, accordingly, the polymerisation speed is alsonot constant over time, that has to be taken into account in themetering speed. The metering speed of the monomer mixture II can bereduced approximately in a linear manner.

2. By metering in an initiator during the reaction, the initiatorconcentration and accordingly also the polymerisation speed can be keptconstant. Thus, the metering in of the monomer mixture II can also beeffected in a manner that is constant over time.

Since monomers are introduced continuously into the reaction vessel inthe case of this copolymer synthesis but no product is discharged(semi-batch operation), the reaction has to be stopped.

In case 1, that occurs automatically since the initiator concentrationfalls to zero. In case 2, the metering in of the monomers, or of theinitiator, has to be stopped. When metering is complete, the monomersstill remaining react to completion to form non-statistical copolymers.That quantity of residual monomers is determined by the batch size attime t=0, which is why the latter should be as small as possible.

In the case of terpolymerisation, approximately the same process can beapplied. Especially advantageous conditions for the purpose prevail whenthe third monomer (b), for example HEMA, GMA, CHOMA, etc., is relatedchemically to the second monomer, for example MMA (b), and, duringcopolymerisation, behaves similarly to the vinyl lactam (a) used, forexample N-vinylpyrrolidone, that is to say, exhibits a similarcopolymerisation parameter.

As mentioned, the composition of the monomer components in a monomermixture II corresponds to the desired final composition of a copolymer.The composition of the monomer mixture I can be calculated therefromusing the Lewis-Mayo relationship.

The preparation of a copolymer according to the invention can be carriedout in the presence or absence of a solvent. A suitable solvent is inprinciple any solvent that dissolves both an uncross-linked copolymerand one of the vinyl monomers (a), (b) and (c) used and is substantiallyinert towards them. Examples are water, alcohols, such as loweralkanols, for example ethanol or methanol, and also carboxylic acid amides, such as dimethylformamide or dimethyl sulfoxide, ethers, such as,for example, diethyl ether, THF or diglymes, also mixtures of suitablesolvents, such as, for example, mixtures of an alcohol and an ether,such as, for example, ethanol/THF, or methanol/diethyl ether. It ispreferable to use lower alkanols, for example ethanol or methanol.

The composition of a copolymer according to the invention, after it hasbeen cross-linked, decides the characteristics of a resulting moulding,such as, for example, a hydrogel contact lens. The ratio of hydrophilicto hydrophobic building blocks (a), (b) and (c) in a copolymer can beused especially to control the mechanical properties of a contact lens.The water content, for example of a hydrogel contact lens, isdetermined, for example, by the content of vinyl lactam, for exampleN-vinyl-2-pyrrolidone, in the copolymer. Hydrophilic vinyl monomers,such as, for example, HEMA or methacrylic acid, can also be used tocontrol the water content in a hydrogel.

A possible method of controlling the molecular weight of a copolymer isto use a regulator during synthesis. A preferred regulator is a loweralkanol, such as, for example, methanol or ethanol, which can be usedsimultaneously, for example, as solvent in the synthesis.

When it has been produced, a copolymer according to the invention can bepurified using customary methods, for example by dissolving andreprecipitating, filtering, removing residual monomers in vacuo,optionally at elevated temperature. Any solvent used can be removedusing a rotary evaporator or by casting and drying a film in air or invacuo. An especially elegant method is purification by ultrafiltrationfor the removal of low-molecular-weight portions and thus also simpleadjustment of the desired concentration of the aqueous copolymersolution.

The present invention relates also to the preparation of hydrogelcontact lenses having final geometry and final water content that areobtainable from aqueous solution within seconds, comprising the steps ofdissolving a statistical copolymer in water and then cross-linking in asuitable manner, for example in a mould. The obvious advantages are:

residual monomers can be removed at the stage of the uncross-linkedcopolymer;

the conversion during cross-linking is substantially lower because thenetwork is made up of polymers and not of monomers;

the reaction times are very short, generally not longer than 1 minuteand typically shorter than 20 seconds; and

a time-intensive extraction of the contact lens with water is no longerimperative because the cross-linking can be effected in water.

Therefore, an aqueous solution is advantageously prepared for thecross-linking of a copolymer according to the invention. If a solventwas used in the synthesis of a copolymer, that solvent can be removedcompletely first of all or only after the addition of a correspondingamount of water. The concentration of a copolymer solution is preferablyso adjusted that the water content of the solution is as near aspossible to that of a finished contact lens. In a preferred method ofpreparation, the water content of an aqueous copolymer solutioncorresponds to the final water content of a cross-linked copolymer, thatis to say, of a hydrogel.

The cross-linking of a copolymer to form the hydrogel is effected as anindependent step and can be carried out in various manners.

A first method consists in exposing a copolymer according to theinvention in suitable form to high-energy radiation, for exampleelectron and gamma rays, and also actinic or UV-radiation, which produceradicals in the copolymer. Those radicals can react to completion toform cross-linked copolymers. With that method of cross-linking, nospecial demands are made in respect of the nature of an uncross-linkedcopolymer according to the invention.

Another possible method consists in using different reaction mechanismsfor the cross-linking on the one hand and for the synthesis of astatistical copolymer on the other. For example, a copolymer may bebuilt up by means of radical polymerisation with thermal initiation,there also being incorporated in the copolymer, for example by a [2+2]cyclo-addition, a monomer building block that can cross-link only whensubjected to UV-radiation. That can be effected, for example, by anN-methacrylic-substituted maleimide, the methacrylic group of which hasbeen copolymerised with, for example, vinylpyrrolidone and another vinylmonomer of a different type.

A further possible method consists in first modifying a copolymer thatcomprises a functional vinyl monomer (b) as building block with areactive monomer (c). According to the definition, the vinylic group ofthe reactive monomer (c) is retained after such a modification. Acopolymer so modified can then be cross-linked, for example, with UVlight of a suitable wavelength, for example in the presence of aphotoinitiator.

A preferred possible method of cross-linking is the photocross-linkingof copolymers disclosed according to claim 1; especially preferred isthe photocross-linking of copolymers disclosed according to claim 1 thathave been modified with a reactive monomer (c).

In the case of photocross-linking, it is suitable to add aphotoinitiator that can initiate radical cross-linking. Examples of suchphotoinitiators are familiar to the person skilled in the art; there maybe mentioned specifically as suitable photoinitiators benzoin methylether, 1-hydroxycyclohexyl phenyl ketone, Darocur and Irgacure types,preferably Darocur 1173® and Irgacure 2959®. Cross-linking can then betriggered by actinic radiation, such as, for example, UV light of asuitable wavelength.

Also suitable are photoinitiators that are incorporated in the copolymerbefore the cross-linking step. Examples of especially suitablephotoinitiators are derivatives of Irgacure 2959® that have beenmodified, for example, with methacrylic acid. A methacrylic acidesterified with, for example, Irgacure 2959® can be incorporated as aspecial monomer into a copolymer. Such a copolymer is then suitable forbeing cross-linked directly, without the addition of a photoinitiator.

Cross-linking is suitably carried out in a solvent. Suitable solventsare in principle any solvents that dissolve copolymers, for examplewater, alcohols, such as lower alkanols, for example ethanol ormethanol, and also carboxylic acid amides, such as dimethyl-formamide ordimethyl sulfoxide, also mixtures of suitable solvents, such as, forexample, mixtures of water and an alcohol, such as, for example, awater/ethanol mixture or a water/methanol mixture.

The cross-linking is preferably carried out directly from an aqueoussolution of a copolymer according to the invention. Such an aqueoussolution can also be obtained directly as the result of a preferredpurification step, for example ultrafiltration. For example, across-linking, preferably a photocross-linking, of an approximately 10to 40% aqueous solution can be carried out.

The present invention relates also to a hydrogel that consistssubstantially of a copolymer in cross-linked form disclosed according toclaim 1.

The present invention relates preferably to a hydrogel consistingsubstantially of a copolymer in cross-linked form disclosed according toclaim 1, the hydrogel being a contact lens.

The present invention relates preferably also to a contact lensconsisting substantially of a copolymer in the cross-linked statedisclosed according to claim 1.

The present invention relates also to a contact lens obtainable bycross-linking a copolymer disclosed according to claim 1.

The following Examples serve to illustrate the present inventionfurther, they are not, however, intended to limit the scope thereof inany way. Temperatures are given in degrees Celsius.

The abbreviations “poly” and “stat” used in connection with thefollowing Examples denote statistical (stat) copolymers (poly).

EXAMPLE 1 Synthesis of poly(N-vinylpyrrolidone-stat-methyl methacrylate)

15.26 g (0.14 mol) of N-vinylpyrrolidone, 0.25 g (2.5 mmol) of methylmethacrylate and 60.55 g of methanol are introduced into a 500 ml brownglass three-necked flask having a stirrer, a Claisen attachment and areflux condenser. The charged apparatus is scavenged with nitrogen viathe reflux condenser, the batch is heated under nitrogen to boilingpoint and a solution of 31.8 mg (0.194 mmol) of AIBN and 1.5 g ofmethanol is added to the batch via a septum using a syringe. Using twoMikrolab M metering units manufactured by Hamilton, a solution Aconsisting of 40.0 g (0.36 mol) of N-vinylpyrrolidone, 18.02 g (0.18mol) of methyl methacrylate and 232.06 g of methanol is metered in at arate of 100 μl per minute and a solution B consisting of 79.5 mg (0.484mmol) of AIBN and 8.95 ml of methanol is metered in at a rate of 9 μlper 99 seconds. After 24 hours, metering is stopped, the batch isallowed to react for a further 16 hours under reflux, is cooled to roomtemperature and the polymer solution is cast to form a film which isthen freed of residual monomers and solvent at 60° C. and 10 Pa (0.1mbar) in a vacuum drying chamber.

Yield: approx. 80-85% of the monomers used.

The polymer dissolves at room temperature in H₂O, CH₃OH and C₂H₅OH (ineach case to the extent of 20% by weight).

EXAMPLE 2 Synthesis of poly(N-vinylpyrrolidone-stat-methylmethacrylate-stat-glycidyl methacrylate)terpolymers

15.26 g (0.14 mol) of N-vinylpyrrolidone, 0.25 g (2.5 mmol) of methylmethacrylate and 60.55 g of methanol are introduced into a 500 ml brownglass three-necked flask having a stirrer, a Claisen attachment and areflux condenser. The charged apparatus is scavenged with nitrogen viathe reflux condenser, the batch is heated under nitrogen to boilingpoint and a solution of 31.8 mg (0.194 mmol) of AIBN and 1.5 g ofmethanol is added to the batch via a septum using a syringe. Using twoMikrolab M metering units manufactured by Hamilton, a solution Aconsisting of 40.0 g (0.36 mol) of N-vinylpyrrolidone, 9.01 g (89.98mmol) of methyl methacrylate, 12.8 g (89.98 mmol) of glycidylmethacrylate and 232.06 g of methanol is metered in at a rate of 200 μlper minute and a solution B consisting of 79.5 mg (0.484 mmol) of AIBNand 8.95 ml of methanol is metered in at a rate of 9 μl per 99 seconds.After 24 hours, metering is stopped, the batch is allowed to react for afurther 16 hours under reflux, is cooled to room temperature and thepolymer solution is cast to form a film. The film is then freed ofresidual monomers and solvent at 60° C. and 10 Pa (0.1 mbar) in a vacuumdrying chamber.

Yield: approx. 80-85% of the monomers used.

The polymers dissolve at room temperature in H₂O, CH₃OH and C₂H₅OH (ineach case to the extent of 20% by weight).

EXAMPLE 3 Synthesis of poly(N-vinylpyrrolidone-stat-methylmethacrylate-stat-hydroxyethyl methacrylate)terpolymers

15.26 g (0.14 mol) of N-vinylpyrrolidone, 0.25 g (2.5 mmol) of methylmethacrylate and 60.55 g of methanol are introduced into a 500 ml brownglass three-necked flask having a stirrer, a Claisen attachment and areflux condenser. The charged apparatus is scavenged with nitrogen viathe reflux condenser, the batch is heated under nitrogen to boilingpoint and a solution of 31.8 mg (0.194 mmol) of AIBN and 1.5 g ofmethanol is added to the batch via a septum using a syringe. Using twoMikrolab M metering units manufactured by Hamilton, a solution Aconsisting of 40.0 g (0.36 mol) of N-vinylpyrrolidone, 9.01 g (89.98mmol) of methyl methacrylate, 11.71 g (89.98 mmol) of hydroxyethylmethacrylate and 232.06 g of methanol is metered in at a rate of 200 μlper minute and a solution B consisting of 79.5 mg (0.484 mmol) of AIBNand 8.95 ml of methanol is metered in at a rate of 9 μl per 99 seconds.After 24 hours, metering is stopped, the batch is allowed to react for afurther 16 hours under reflux, is cooled to room temperature and thepolymer solution is cast to form a film. The film is then freed ofresidual monomers and solvent at 60° C. and 10 Pa (0.1 mbar) in a vacuumdrying chamber.

Yield: approx. 80-85% of the monomers used.

The polymers dissolve at room temperature in H₂O, CH₃OH and C₂H₅OH (ineach case to the extent of 20% by weight).

EXAMPLE 4 Synthesis of poly(N-vinylpyrrolidone-stat-methylmethacrylate-stat-cyclohexene oxide methacrylate)terpolymers

15.26 g (0.14 mol) of N-vinylpyrrolidone, 0.25 g (2.5 mmol) of methylmethacrylate and 60.55 g of methanol are introduced into a 500 ml brownglass three-necked flask having a stirrer, a Claisen attachment and areflux condenser. The charged apparatus is scavenged with nitrogen viathe reflux condenser, the batch is heated under nitrogen to boilingpoint and a solution of 31.8 mg (0.194 mmol) of AIBN and 1.5 g ofmethanol is added to the batch via a septum using a syringe. Using twoMikrolab M metering units manufactured by Hamilton, a solution Aconsisting of 40.0 g (0.36 mol) of N-vinylpyrrolidone, 9.01 g (89.98mmol) of methyl methacrylate, 16.4 g (89.98 mmol) of cyclohexene oxidemethacrylate and 232.06 g of methanol is metered in at a rate of 200 μlper minute and a solution B consisting of 79.5 mg (0.484 mmol) of AIBNand 8.95 ml of methanol is metered in at a rate of 9 μl per 99 seconds.After 24 hours, metering is stopped, the batch is allowed to react for afurther 16 hours under reflux, is cooled to room temperature and thepolymer solution is cast to form a film. The film is then freed ofresidual monomers and solvent at 60° C. and 10 Pa (0.1 mbar) in a vacuumdrying chamber.

Yield: approx. 80-85% of the monomers used.

The polymers dissolve at room temperature in H₂O, CH₃OH and C₂H₅OH (ineach case to the extent of 20% by weight).

EXAMPLE 5 Synthesis of poly(N-vinylpyrrolidone-stat-methylmethacrylate-stat-DMI-O-MA)terpolymers

15.26 g (0.14 mol) of N-vinylpyrrolidone, 0.25 g (2.5 mmol) of methylmethacrylate and 60.55 g of methanol are introduced into a 500 ml brownglass three-necked flask having a stirrer, a Claisen attachment and areflux condenser. The charged apparatus is scavenged with nitrogen viathe reflux condenser, the batch is heated under nitrogen to boilingpoint and a solution of 31.8 mg (0.194 mmol) of AIBN and 1.5 g ofmethanol is added to the batch via a septum using a syringe. Using aMikrolab M metering unit manufactured by Hamilton, a solution consistingof 40.0 g (0.36 mol) of N-vinylpyrrolidone, 9.01 g (89.98 mmol) ofmethyl methacrylate, 25.3 g (89.98 mmol) of DMI-O-MA and 232.06 g ofmethanol is metered in at a rate that decreases in a linear manner(initial rate of 100 μl per minute decreasing to 3 μl per minute). After24 hours, metering is stopped, the batch is allowed to react for afurther 16 hours under reflux, is cooled to room temperature and thepolymer solution is cast to form a film. The film is then freed ofresidual monomers and solvent at 60° C. and 10 Pa (0.1 mbar) in a vacuumdrying chamber.

Yield: approx. 80-85% of the monomers used.

The polymer dissolves at room temperature in H₂O, CH₃OH and C₂H₅OH (ineach case to the extent of 20% by weight).

EXAMPLE 6 Synthesis of poly(N-vinylpyrrolidone-stat-methylmethacrylate-stat-2-hydroxyethyl methacrylate)terpolymers

15.26 g (0.14 mol) of N-vinylpyrrolidone, 0.25 g (2.5 mmol) of methylmethacrylate and 60.55 g of methanol are introduced into a 500 ml brownglass three-necked flask having a stirrer, a Claisen attachment and areflux condenser. The charged apparatus is scavenged with nitrogen viathe reflux condenser, the batch is heated under nitrogen to boilingpoint and a solution of 31.8 mg (0.194 mmol) of AIBN and 1.5 g ofmethanol is added to the batch via a septum using a syringe. Using aMikrolab M metering unit manufactured by Hamilton, a solution consistingof 40.0 g (0.36 mol) of N-vinylpyrrolidone, 9.01 g (89.98 mmol) ofmethyl methacrylate, 11.71 g (89.98 mmol) of 2-hydroxyethyl methacrylateand 232.06 g of methanol is metered in at a rate that decreases in alinear manner (initial rate of 200 μl per minute decreasing to 6 μl perminute). After 24 hours, metering is stopped, the batch is allowed toreact for a further 16 hours under reflux, is cooled to room temperatureand the polymer solution is cast to form a film. The film is then freedof residual monomers and solvent at 60° C. and 10 Pa (0.1 mbar) in avacuum drying chamber.

Yield: approx. 80-85% of the monomers used.

OH group content: approx. 1.00 (mmol OH)/g

The polymer dissolves at room temperature in H₂O, CH₃OH and C₂H₅OH (ineach case to the extent of 20% by weight).

EXAMPLE 7 Synthesis of poly(N-vinylpyrrolidone-stat-methylmethacrylate-stat-2-hydroxyethylmethacrylate-stat-1,1-dimethyl-2-oxo-2-{4-[[[(3,5,5-trimethyl-3-methylaminomethyl-cyclohexyl)-amino]-carbonyl]-ethoxy]-phenoxy}-ethylmethacrylate)

3.92 g (35.3 mmol) of N-vinylpyrrolidone, 0.031 g (0.312 mmol) of methylmethacrylate, 0.045 g (0.35 mmol) of 2-hydroxyethyl methacrylate, 0.007g (0.012 mmol) of1,1-dimethyl-2-oxo-2-{4-[[[(3,5,5-trimethyl-3-methylaminomethyl-cyclohexyl)-amino]-carbonyl]-ethoxy]-phenoxy}-ethylmethacrylate and 15.97 g of methanol are introduced into a 250 ml brownglass three-necked flask having a stirrer, a Claisen attachment and areflux condenser. The charged apparatus is scavenged with nitrogen viathe reflux condenser, the batch is heated under nitrogen to boilingpoint and a solution of 8.0 mg (0.049 mmol) of AIBN and 0.38 g ofmethanol is added to the batch via a septum using a syringe. Using aMikrolab M metering unit manufactured by Hamilton, a solution consistingof 5.0 g (44.99 mmol) of N-vinylpyrrolidone, 1.13 g (11.25 mmol) ofmethyl methacrylate, 1.46 g (11.24 mmol) of 2-hydroxyethyl methacrylate,0.46 g (0.79 mmol) of1,1-dimethyl-2-oxo-2-{4-[[[(3,5,5-trimethyl-3-methylaminomethyl-cyclohexyl)-amino]-carbonyl]-ethoxy]-phenoxy}-ethylmethacrylate and 32.18 g of methanol is metered in at a rate thatdecreases in a linear manner (initial rate of 100 μl per minutedecreasing to 10 μl per minute). After 24 hours, metering is stopped,the batch is allowed to react for a further 16 hours under reflux and iscooled to room temperature. The solution is introduced into 450 ml ofacetone, the polymer precipitating in the form of a sticky solid. Thesupernatant solution is decanted and the residue is dried in a vacuumdrying chamber to give the compound named in the title.

EXAMPLE 8 Synthesis of poly(N-vinylpyrrolidone-stat-2-hydroxyethylmethacrylate-stat-glycidyl methacrylate)

15.26 g (0.14 mol) of N-vinylpyrrolidone, 0.33 g (2.5 mmol) of2-hydroxyethyl methacrylate and 60.55 g of methanol are introduced intoa 500 ml brown glass three-necked flask having a stirrer, a Claisenattachment and a reflux condenser. The charged apparatus is scavengedwith nitrogen via the reflux condenser, the batch is heated undernitrogen to boiling point and a solution of 31.8 mg (0.194 mmol) of AIBNand 1.5 g of methanol is added to the batch via a septum using asyringe. Using two Mikrolab M metering units manufactured by Hamilton, asolution A consisting of 40.0 g (0.36 mol) of N-vinylpyrrolidone, 11.7 g(89.98 mmol) of 2-hydroxyethyl methacrylate, 12.8 g (89.98 mmol) ofglycidyl methacrylate and 232.06 g of methanol is metered in at a rateof 200 μl per minute and a solution B consisting of 79.5 mg (0.48 mmol)of AIBN and 8.95 ml of methanol is metered in at a rate of 9 μl per 99seconds. After 24 hours, metering is stopped, the batch is allowed toreact for a further 16 hours under reflux, is cooled to room temperatureand the polymer solution is cast to form a film. The film is then freedof residual monomers and solvent at 60° C. and 10 Pa (0.1 mbar) in avacuum drying chamber.

Yield: approx. 80-85% of the monomers used.

The polymer dissolves at room temperature in H₂O, CH₃OH and C₂H₅OH (ineach case to the extent of 20% by weight).

EXAMPLE 9 Synthesis of poly(N-vinylpyrrolidone-stat-2-hydroxyethylmethacrylate-stat-cyclohexene oxide acrylate)

15.26 g (0.14 mol) of N-vinylpyrrolidone, 0.33 g (2.5 mmol) of2-hydroxyethyl methacrylate and 60.55 g of methanol are introduced intoa 500 ml brown glass three-necked flask having a stirrer, a Claisenattachment and a reflux condenser. The charged apparatus is scavengedwith nitrogen via the reflux condenser, the batch is heated undernitrogen to boiling point and a solution of 31.8 mg (0.194 mmol) of AIBNand 1.5 g of methanol is added to the batch via a septum using asyringe. Using two Mikrolab M metering units manufactured by Hamilton, asolution A consisting of 40.0 g (0.36 mol) of N-vinylpyrrolidone, 11.7 g(89.98 mmol) of 2-hydroxyethyl methacrylate, 16.4 g (89.98 mmol) ofcyclohexene oxide acrylate and 232.06 g of methanol is metered in at arate of 200 μl per minute and a solution B consisting of 79.5 mg (0.48mmol) of AIBN and 8.95 ml of methanol is metered in at a rate of 9 μlper 99 seconds. After 24 hours, metering is stopped, the batch isallowed to react for a further 16 hours under reflux, is cooled to roomtemperature and the polymer solution is cast to form a film. The film isthen freed of residual monomers and solvent at 60° C. and 10 Pa (0.1mbar) in a vacuum drying chamber.

Yield: approx. 80-85% of the monomers used.

The polymer dissolves at room temperature in H₂O, CH₃OH and C₂H₅OH (ineach case to the extent of 20% by weight).

EXAMPLE 10 Functionalisation of poly(N-vinylpyrrolidone-stat-glycidylmethacrylate) with methacrylic acid

Two 3.0 g portions of the polymer of Example 3 (2.56 mmol of epoxygroups) are dissolved in 30 g of DMF (anhydrous) and each solution isstabilised with approximately 11 mg of hydroquinone. 442.9 mg (5.12mmol) of methacrylic acid are then added to each solution (in each casetwice the molar amount based on the epoxy group content, which isdetermined by titration of the polymer in glacial acetic acid in thepresence of tetrabutyl-ammonium bromide with 0.1 molar perchloric acid)and heating is effected to 100° C. 3.33 g of Al₂O₃ are then added to onesolution and 4.4 mg of FeCl₃ are added to the second solution, and astream of dry air is passed over the reaction solutions. After areaction time of from 6 to 10 hours, insoluble portions are filtered offwhile hot via a Büchner funnel, and the epoxy content of the solutionsis again determined by titration. The volatile portions of the reactionsolutions are distilled off under a high vacuum at 40° C. and theresidues are dissolved in water. The aqueous solutions are freed ofresidual monomers by ultrafiltration and then concentrated to thedesired solids contents.

Degree of reaction with Al₂O₃: approx. 33%

Degree of reaction with FeCl₃: 17-18%

The polymer dissolves at room temperature in H₂O, CH₃OH and C₂H₅OH (ineach case to the extent of 20% by weight).

EXAMPLE 11 Functionalisation of poly(N-vinylpyrrolidone-stat-glycidylmethacrylate) with 2-hydroxyethyl methacrylate

Two 3.0 g portions of the polymer of Example 3 (2.56 mmol of epoxygroups) are dissolved in 30 g of DMF (anhydrous) and each solution isstabilised with approximately 11 mg of hydroquinone. 668.2 mg (5.12mmol) of 2-hydroxyethyl methacrylate are added to each solution (in eachcase twice the molar amount based on the epoxy group content, which isdetermined by titration of the polymer in glacial acetic acid in thepresence of tetrabutylammonium bromide with 0.1 molar perchloric acid)and heating is effected to 100° C. 3.33 g of Al₂O₃ are then added to onesolution and 7.3 mg of FeCl₃ are added to the second solution, and astream of dry air is passed over the reaction solutions. After areaction time of from 6 to 10 hours, insoluble portions are filtered offwhile hot via a Büchner funnel, and the epoxy content of the solutionsis again determined by titration. The volatile portions of the reactionsolutions are distilled off under a high vacuum at 40° C. and theresidues are dissolved in water. The aqueous solutions are freed ofresidual monomers by ultrafiltration and then concentrated to thedesired solids contents.

Degree of reaction with Al₂O₃: approx. 33%

Degree of reaction with FeCl₃: 17-18%

The polymer dissolves at room temperature in H₂O, CH₃OH and C₂H₅OH (ineach case to the extent of 20% by weight).

EXAMPLE 12 Functionalisation of poly(N-vinylpyrrolidone-stat-methylmethacrylate-stat-2-hydroxyethyl methacrylate) with methacrylic acidchloride

2.18 g of the polymer of Example 6 named in the title (2.18 mmol of OHgroups) are dissolved in 30.63 g of dimethylacetamide, and 5 mg ofhydroquinone and 419 μl (4.29 mmol) of methacrylic acid chloride areadded. The reaction mixture is heated for 4 hours at 80° C. and, afterthat period, the batch is allowed to cool and 100 ml of acetone areadded thereto. The solution is introduced into 400 ml of acetone, thepolymer precipitating in the form of a sticky solid. The supernatantsolution is decanted and the residue is dried in a vacuum dryingchamber.

Yield after precipitation: 1.39 g (53% of the theoretical yield)

The polymer is soluble in H₂O, CH₃OH and C₂H₅OH (in each case to theextent of 30% by weight).

EXAMPLE 13 Functionalisation of poly(N-vinylpyrrolidone-stat-methylmethacrylate-stat-2-hydroxyethylmethacrylate-stat-1,1-dimethyl-2-oxo-2-{4-[[[(3,5,5-trimethyl-3-methylaminomethyl-cyclohexyl)-amino]-carbonyl]-ethoxy]-phenoxy}-ethylmethacrylate) with methacrylic acid chloride

2.01 g of the polymer of Example 7 named in the title (2.98 mmol of OHgroups) are dissolved in 30.13 g of dimethylacetamide, and 5 mg ofhydroquinone and 583 μl (5.97 mmol) of methacrylic acid chloride areadded. The reaction mixture is heated for 4 hours at 80° C. and, afterthat period, the batch is allowed to cool and 100 ml of acetone areadded thereto. The solution is introduced into 400 ml of acetone, thepolymer precipitating in the form of a sticky solid. The supernatantsolution is decanted and the residue is dried in a vacuum dryingchamber.

Yield after precipitation: 1.39 g (53% of the theoretical yield)

EXAMPLE 14 Cross-linking of the Polymer of Example 12

An 18% aqueous solution (a) and a 30% aqueous solution (b) are preparedfrom the functionalised polymer of Example 12, and 0.3% (based on theamount of polymer) of Darocur 2959® is added to each of the twosolutions. The solutions are introduced into polypropylene (PP) mouldshaving lens geometry and the filled moulds are irradiated for 12 secondswith a 500 W Hg high pressure lamp for example Oriel type no. 6285). Thecross-linked copolymers are then caused to swell in physiological salinesolution, there being formed from

a) 18% by weight of colloidal solution (sol, uncross-linked) a hydrogelwith 90% by weight of water, and from

b) 30% by weight of colloidal solution (sol, uncross-linked) a hydrogelwith 83% by weight of water.

The hydrogels a) and b) are finished contact lenses.

EXAMPLE 15 Cross-linking of the Polymer of Example 13

A 10% aqueous solution is prepared from the functionalised polymer ofExample 13. The solution is introduced into PP moulds having lensgeometry and the filled moulds are irradiated for 60 seconds with a 500W Hg high pressure lamp (for example Oriel type no. 6285).

Cross-linked hydrogels in the form of contact lenses are produced.

EXAMPLE 16 Functionalisation of poly(N-vinylpyrrolidone-stat-methylmethacrylate) with 2-hydroxyethyl methacrylate

4.0 g of the polymer of Example 1 named in the title and 54 mg ofhydroquinone are dissolved in 16 g of dimethylacetamide, and 18.22 g(0.14 mol) of 2-hydroxyethyl methacrylate and 23.6 mg (0.037 mmol) ofdibutyltin dilaurate are added. The batch is introduced into adistillation apparatus, a weak stream of dried air is passed through thereaction solution and the latter is heated for 18.5 hours at 85° C. Thebatch is cooled to room temperature and the polymer is precipitated bythe addition of approximately 80 ml of acetone. The supernatant solutionis decanted and the polymer is dried in a vacuum exsiccator at roomtemperature and 10 Pa.

Yield: approx. 76% of the monomers used.

The polymer is soluble in H₂O, CH₃OH and C₂H₅OH (in each case to theextent of 30% by weight).

EXAMPLE 17 Cross-linking of the Polymer of Example 16

1.00 g of the polymer of Example 16 is dissolved in 2.33 ml of water(approximately 30% by weight), and 16.7 mg of Darocur® 2959 are added.The solution is introduced into a PP mould having lens geometry and theclosed mould is irradiated for 1 minute with an Hg high pressure lamp. Ahydrogel is produced in the form of a moulding.

EXAMPLE 18 Synthesis of poly(N-vinylpyrrolidone-stat-2-hydroxyethylmethacrylate-stat-2-aminoethyl methacrylate hydrochloride)

15.26 g (0.14 mol) of N-vinylpyrrolidone, 0.22 g (1.67 mmol) of2-hydroxyethyl meth- acrylate, 0.28 g (0.83 mmol) of a 50 % aqueoussolution of 2-aminoethyl methacrylate hydrochloride and 60.55 g ofmethanol are introduced into a 500 ,l brown glass three- necked flaskhaving a stirrer, a Claisen attachment and a reflux condenser. Thecharged apparatus is scavenged with nitrogen via the reflux condensor,the batch is heated under nitrogen to boiling point and a solution of31.8 mg (0.194 mmol) of AIBN and 1.5 g of methanol is added to the batchvia a septum using a syringe. Using two Mikrolab M metering unitsmanufactured by Hamilton, a solution A consisting of 40.0 g (0.36 mol)of N-vinylpyrrolidone, 15.6 g (120 mmol) of 2-hydroxyethyl methacrylatehydrochloride and 232.06 g of methanol is metered in at a rate of 200 μlper minute and a solution B consisting of 79.5 mg (0.48 mmol) of AIBNand 8.95 ml of methanol is metered in at a rate of 9 μl per 99 seconds.After 24 hours, metering is stopped, the batch is stirred for a further16 hours under reflux, is then cooled to room temperature and theresidual monomers and solvent are separated off by ultrafiltration usinga 3 kDalton PES (poly-ether sulfone) membrane under an operatingpressure of 2.5 · 10⁵ Pa, the solvent being replaced by water.

Yield: approx. 80-85 % of the monomers used.

The polymer dissolves at a room temperature in H₂O, CH₃OH and C₂H₅OH (ineach case to the extent of 30 % by weight).

EXAMPLE 19 Functionalism of poly(N-vinylpyrrolidone-stat-2-hydroxyethylmethacrylate-stat-2-aminoethyl methacrylate hydrochloride)

1.0 g of the polymer of Example 18 is dissolved in 2.33 ml of water. Thesolution is titrated with 0.1N sodium hydroxide solution to pH 10, andthen 0.036 g (0.23 mmol) of isocyanatoethyl methacrylate is added, withstirring. The reaction conversion is monitored by recording the pH value(pH-monitoring).

EXAMPLE 20 Cross-linking of poly(N-vinylpyrrolidone-stat-2-hydroxyethylmethacrylate-stat-2-aminoethyl methacrylate hydrochloride)functionalised with isocyanatoethyl methacrylate

16.7 mg of Irgacure 2959® are added to the aqueous polymer solution ofExample 19 and then the batch is introduced into PP moulds having lensgeometry. The closed PP moulds are then irradiated for 10 seconds with a500 W Hg high pressure lamp. Finished contact lenses are thus obtainedin the form of hydrogels having a water content of approximately 85%.

What is claimed is:
 1. A process for the preparation of a water-solublecross-linkable copolymer having a desired copolymer composition, whereina vinyl lactam (a) and at least one further vinyl monomer (b) of adifferent type selected from the group consisting of hydrophobic,hydrophilic and functional vinyl monomers are present in said copolymerin the form of statistically distributed building blocks in accordancewith the Lewis-Mayo equation; said process comprising the steps ofplacing a first monomer mixture (I) the composition of which gives thedesired copolymer composition in accordance with the Lewis-Mayo equationin a reaction vessel, initiating polymerisation with an initiator and,after polymerisation has been initiated, metering in a second monomermixture (II) the composition of which corresponds to the desiredcopolymer composition and the metering speed is in accordance with theconsumption of the monomers such that the concentration of the monomersand ratio of the monomers are constant during the reaction.
 2. A processaccording to claim 1, wherein the concentration of the monomers is keptconstant during the reaction by reducing in a linear manner the meteringspeed of the monomer mixture (II) in accordance with the increasing timeof the reaction.
 3. A process according to claim 1 wherein theconcentration of the monomers is kept constant during the reaction bymetering in the initiator in a constant linear manner during thereaction.
 4. A hydrogel article produced by crosslinking in a mould acopolymer produced by the process according to claim 1 in aqueoussolution.
 5. A hydrogel according to claim 4 that is a contact lens. 6.A process for the preparation of a hydrogel article wherein saidhydrogel article is produced by crosslinking a copolymer produced by theprocess according to claim 1 in aqueous solution in a mould.
 7. Aprocess according to claim 6 wherein the concentration of the aqueoussolution corresponds to the final water content of the hydrogel.
 8. Aprocess according to claim 6 wherein the cross-linking is effected withUV light.
 9. A process according to claim 6 wherein the hydrogel is acontact lens with a final water content and a final geometry.
 10. Acontact lens comprising a copolymer produced by the process according toclaim 1 wherein said copolymer is crosslinked.
 11. A process accordingto claim 1, wherein a functional vinyl monomer is present in saidcopolymer as a building block, said copolymer is modified with areactive vinyl monomer (c), the reactive group of said reactive vinylmonomer (c) reacting with the functional group of said functional vinylmonomer to form a covalent bond and the vinylic group of said reactivevinyl monomer (c) being retained.